460 Ford Forum banner

Main Bearing Clearances

25K views 43 replies 19 participants last post by  bbfstanger 
#1 ·
I am putting my engine back together and checked the main bearing clearances. Crank is ground .010 under. Bearings Clevite 77 MS-1039P-10

#1 - Crank Journal = 2.9892 - Clearance = .0034"
#2 - Crank Journal = 2.9891 - Clearance = .0034"
#3 - Crank Journal = 2.9894 - Clearance = .0044"
#4 - Crank Journal = 2.9894 - Clearance = .0034"
#5 - Crank Journal = 2.9891 - Clearance = .0036

Measured using mics with bearings installed and caps torqued.
This is on a 460 build, expecting 500 HP, 550 TQ, 6000RPM

These clearances seem loose to me. Any advise?
 
#4 ·
For that sort of rpm level I think you would be a lot better with a full .001 less bearing clearance. Since you're at .010 on your bearings and crankshaft you have two options as Randy said, getting another crank and having it ground to fit your block, in your case .009 undersize. Or have it line honed to make the housings .001 smaller than they are right now.
 
#5 ·
I agree with what both Randy and Dave have said.

Furthermore with the way bearings are nowadays, in terms of quality control in regards to sizing, you can probally go buy a different brand of .010" bearings, say Federal Mogul for example, and come up with a totally different set of dimensions. Then if you consider coated and uncoated bearings, that will change things again.

We cannot build an engine around here, without having several sets of bearings on hand to choose from. It's a trial and error deal nowadays, and I don't care if it's a Ford, Chevy or Mopar engine that you are building.

The performance enthusiast who is building his own engine, and is the type of guy who maybe builds only one engine in three or four years, should NOT expect that one set of rod and main bearings that comes in a stroker kit from Hawks, Flatlander or others, is going to provide the correct clearances out of the box.

Before you go adjusting your block main journal i.d. smaller, or before you go find another crankshaft, may I suggest that you buy another set of bearings, of a different brand and try them.

Hope this helps,
 
#6 ·
Yes I'd like to see a full .001 less. According to my manual, the factory specs are .001 to .002.

I guess another option is to grind the crank to .019 under and get a set of .020 under bearings.

Probably line honing is the right way to go.

I'll discuss with the machine shop on Monday.
 
#7 ·
Sorry Charlie, I must have been posting my response when you posted yours.

I am surprised that you can find that much difference in bearings.

Problem is as you know, I can't return the bearings once they have been opened.

But I'll discuss that with the machine shop on Monday as well.

Thanks
 
#9 ·
When I do stroker kits I offer an exhange on bearings for just that reason. I try to keep the odd sizes in stock - but for a .010 under crank you are in trouble. Line hone or another crank...

I set up .009s and .011s for the Chevy stuff back when I was at F-M, but they were not going to let me do that for the less popular applications
 
#10 ·
:lol: Ok guys, I am missing something here. How can you make the block journals smaller by honing? And are his tolerances between the block and bearings, or between the bearings and cranks? I would think they are between the bearings and the crank!?! I know I sound ignorant, but I am not a pro, I am just a little confused. I'm thinking that if you put the caps on and torque them down, then hone the block, you are going to make the "hole" bigger?!?!?! :roll: Please, tell me what I am missing!!!!!! :roll:
 
#11 ·
He cuts a little bit off the main cap first - then hones the hole to a slightly smaller diameter - more bearing crush and hopefully a teeny bit tighter clearance....
 
#12 ·
Randall,

What you do is;

1. Cut some (very small amount) off of the bottom of the main caps. Sunnen makes a machine for this.

2. Then bolt the caps back on and the hole should now be eliptical, with the 12:00 to 6:00 dimension be smaller than the 3:00 to 9:00 dimension.

3. Then you go back and line hone the block to the low side of the main housing bore spec. This will tighten up the main bearing clearance.

Hope this helps,
 
#15 ·
Crank

Your crank is dead on what I want my grinds and new cranks to mic. About 5 tenths under is what I consider perfect. After checking thousands of factory cranks for many years, this is what is coming out of the factories as the typical std. What they have and we do not is a full stock of hand fit bearings. For my own use I love .003 to .0035 but I do not use ant piss for oil.
Van
 
#16 ·
OK I found a listing for Kings at:
http://www.king-bearings.com/cat/panel/pan1243.htm

Set MB5242HP lists .011 Bearing
This set is 3/4 grooved.
Is that set OK?

I also see Set MB5512SI full grooved like my originals. It says "all undersizes" but does not specifically list .011's like the 1st set. So I don't know if they are available.

Anyone here want to sell me a set?
 
#20 ·
I am confused and would like Lem, Barry or Randy to help me understand.

I would have though that IF I had a crank (.010/.010) that was turned too small or a main saddle that was honed too large and I was trying to take up the extra clearance with a +.001 bearing that I would need a .011 bearing if my clearances were too large (or a .009 if my clearances were too tight).

Help me understand why everyone is talking about a .009 bearing to solve this problem.

Thanks again - it is just curiosity for me as I am just trying to continue to learn and understand from the experts here.
 
#23 ·
Lem Evans said:
King makes an .009"....you may want to check with them...they may offer a .011" also .
You could have a set of .010" coated...it'll take uo about .0005"
Lem
Can you give me the part number for the .009 bearings?
Thanks
 
#24 ·
Chuck Stevens said:
If you have a -.010 crank, a .009 bearing will be tighter (less clearance). :roll:
Chuck (el al)

I was pretty sure that was what Lem meant in his earlier reply.
I know the he knows what he was talking about - so my question was "WHY" do they number them that way when it seems backwards to the less informed.

Is there a reason that they came up with this wonderfully intuiative numbering system? The best reason I can come up with is it is a .010 under bearing (-.010) that they have add .001 extra material to. But IF the bearing is for a .010 under crank - then you would expect it to have .010 more material than a standard crank bearing - wouldn't you? Then if you added another .001 to that wouldn't it be .011?

I guess it is just one of those things that you have to remember is backwards in life.


Thanks again.
 
#26 ·
A .010 under crank means that the journal has been machine down undersized by .010".

Accordinally you should order a .010 undersized bearing. That bearing is thicker than the original to allow for the undersized crank and maintain original bearing clearances.

In my case I have excessive clearance so I am looking for a bearing that is a little thicker than a .010" under bearing. Thus a .011" under bearing would be a little thicker than a .010 under bearing and give me the proper clearance.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top